China has announced it will limit oil supplies to North Korea under U.N. sanctions, stepping up pressure on Pyongyang over its pursuit of nuclear and missile technology.

The Commerce Ministry said Saturday that China, the North’s main trading partner and energy supplier, will limit supplies of refined petroleum products starting Oct. 1. It said Beijing also will ban imports of North Korean textiles, one of Pyongyang’s last major sources of foreign revenue following repeated rounds of U.N. sanctions.

China has long been the North’s only major ally and diplomatic protector but is expressing increasing frustration with the government of Kim Jong Un. Beijing’s status as the North’s main trading partner makes its cooperation critical to the success of economic sanctions.